1. Field of the Invention
Embodiments of the present invention relate to ultrasound imaging probes, and particularly, to flexible, capacitive micromachined ultrasonic transducer (CMUT) based guidewire ultrasound imaging probes using CMUT arrays integrated with Complementary metal-oxide-semiconductor (CMOS) electronics, and integration of pressure (e.g. fractional flow reserve (FFR)) sensors with the same imaging probe.
2. Background of Related Art
Side-looking intravascular ultrasound (“IVUS”) imaging probes exist that provide relatively high resolution images of tissue and fluid. This can be useful, for example, when inspecting the inside surfaces of vessels or tissues immediately surrounding the vessel.
In order to navigate tortuous arteries and coronary structures, for example, an important aspect of IVUS probes is the size and flexibility of the probes. As a result, the rigid section of the probe close to the imaging tip should be as short as small in diameter as possible. Current ultrasound array probes used for these purposes are rigid over several mm, limiting their maneuverability.
During cardiac or other vascular procedures, the surgeon first inserts a guidewire in to the desired artery, sometimes anchoring it in place. The surgeon then uses a series of catheters that are “threaded” over the guidewire. In order to change catheters, e.g., from a balloon catheter to an imaging catheter, the first catheter must be completely removed and the second catheter inserted. This must be done carefully to avoid injuring the vessels walls and thus, can take a significant amount of time—generally 15-20 minutes. Both the extra time involved and the increased risk of incidental injury increase the risks associated with the procedure. As a result, while IVUS greatly improves the outcome of intravascular procedures, for example, it is only used in approximately 20% of intravascular procedures.
In contrast, guidewires are used in nearly 100% of intravascular procedures. Thus, an imaging array integrated into a standard guidewire would eliminate the need to change catheters during the procedure. The surgeon could simply image the vessel as the guidewire is being inserted, during the interventional procedure or after the procedure without a need to exchange catheters. This would improve the outcome of intravascular procedures with no increase in the time or risks associated with removing and inserting multiple catheters.
To maintain the flexibility and mechanical properties of the guidewire, however, the number of electrical connections connecting the probe electronics to the back end imaging system should be limited. In other words, a larger number of cables would make the guidewire thicker and less flexible. The number of external connections is also important, for example, because it adversely affects the mechanical performance of the guidewire if the core of the guidewire is thinned down to make space for the electrical connection wires without increasing the diameter of the guidewire.
In addition to size constraints, ultrasound probes typically must limit their power consumption. When the probe is activated, the temperature of the probe must be limited to prevent damage to surrounding tissue, or simply to prevent the probe from overheating when in open air. In some instances, for example, the probe may remain active outside the body. In this instance, power consumption should be limited to prevent the probe electronics from overheating and damaging the mechanical structure of the probe such as the adhesion layers or coatings.
Measurement of pressure in the blood vessels to obtain FFR information has proven to be useful in evaluating the treatment options in cardiovascular interventions. Therefore, integrating this functionality to the IVUS imaging guidewire is desirable because it enables the use of a single guidewire to better evaluate the condition of the blood vessels.
What is needed, therefore, is a CMUT-CMOS integrated ultrasonic probe on a standard guidewire-sized package. The probe should include reduced power consumption through custom electronics design and intelligent power management. The probe should comprise improved resolution with minimal cross-sectional area and interconnects along the catheter. The probe may also include an integrated FFR sensor to or Doppler sensor to measure blood pressure and/or flow while providing ultrasound imaging. It is to such an ultrasonic probe that embodiments of the present invention are primarily directed.